Circuit-breaker or line-opener.



UNITED STATES PATENT OFFICE.

FREDERICK O. ROBERTSON, OF TORONTO, CANADA.

CIRCUIT-BREAKER OR LINE-OPENER.

SPECIFICATION forming part of Letters Patent No. 639,688, dated December19, 18992 Application filed June 25, 1898. Serial No. 684,506. No model)To all whom it may concern:

Be it known that 1, FREDERICK CHARLES ROBERTSON, residing at Toronto, inthe county of York and Province of Ontario, Canada, have invented a newand useful Improvement in Circuit-Breakers or Line-Openers, of which thefollowing is a specification.

My invention relates to improvements in circuit-breakers or line-openersof the fusible- Wire type, adaptable to any telegraph, telephone, orother 1ow-current electric circuit, and has for its object to cause thefusible wire to melt with certainty and open the circuit betweenline-wire and instrument whenever the current in said circuit becomesaugmented to such a dangerous degree as to cause overheating of themagnet-wire of the instruments in circuit through accidental crossing ofsaid line-wire with another line carrying a current of high voltage,such as an electric-light or trolley line.

It is the general practice to protect the instruments on telephone andtelegraph circuits against damage liable to be caused by said circuitsbecoming crossed with an electriclight line, trolley, or other circuitof high voltage by inserting in said telephone or telegraph circuit,between the line-wire and instruments, a section of fusible wire, whichwhen'the current in said circuit becomes abnormally increased to adangerous degree, due to leakage thereto of current from a circuit ofhigh voltage, will become overheated and melt, thereby opening thecircuit. It frequently occurs, however, with circuits thus protectedthat owing to the resistance of the instruments therein the abnormalcondition of the current brought about by said accidental crossing doesnot attain sufficient strength to cause the fusible wire to melt, but atthe same time becomes sufficiently strong to dangerously overheat themagnet-winding of the said instruments.

The object of my invention is to provide a means whereby the instrumentsprotected will be cut out of circuit within a brief period after thecurrent in said circuit becomes abnormally increased. The effectproduced by cutting said instruments out of circuit will be to allow thecurrent through the fusible wire to attain a higher degree of strength,causing it to melt more readily. A device has been invented with a viewof producing this result. In such device the cutting out of theinstruments at the time the current has assumed an abnormally highdegree is effected by the adoption of a relay-magnet interposed incircuit between the fusible wire and protected instrument and soadjusted that its armature will only be attracted when the currentbecomes abnormally increased. The 10- cal contact-points of said relaywhen closed complete a subsidiary circuit between fusible wire andground. In my device there are no electromagnets, the cutting out of theinstruments being effected in an entirely different manner, and iteffectively operates should the incoming foreign current be either of adirect or alternating character, and to effect this result I make use ofa bar or tube com posed of a material capable of expanding whenheatedsuch as vulcanite, hard rubher, or other similar co mpositionandhaving wound on its surface a wire of comparatively high specificresistance, said wire forming part of the circuit between fusible wireand instrument to be protected. The said bar or tube of expansiblematerial being thus placed in close proximity to said resistancewireabsorbs heat therefrom, which is generated in said wire by the action ofthe current when abnormally increased. The effect of the heat thusabsorbed from said wire will be to cause the bar ortube to expand andlengthen. Two contact-points are provided,one of which is secured to oneend ofsaid bar or tube. The other contact-point is secured to the otherend of said bar or tube through the medium of a bar, tube, or platecomposed of similar material and so placed as to be unaffected by theheat generated in said resistance-wire. One of said contact-points iselectrically connected to the circuit at a point between the fusiblewire and resistance-wire, the other'contactpoint being connected to aground-wire, said contact-points being so adjusted that under the normalcondition of the circuit they remain separated by an air-gap; but shouldthe current in the circuit become augmented through leakage thereto of aforeign current of high voltage the resistance-wire becomes heated,which imparts heat to the eXpansible bar or tube, causing it to expandand the contact-points to come together, thus closing the subsidiarycircuit between the fusible wire and earth. The short circuit to earththus being formed enables the current to attain a higher value, whichcauses the fusible wire to melt and open the circuit, after which theexpanded bar or tube contracts as it cools and finally resumes itsnormal condition separating the contact-points.

The invention is more fully described, and more particularly pointed outin the claims.

In the drawings, Figure 1 is a side view of the device, partly shown inlongitudinal sec tion, arranged to protect a single circuit. Fig. 2 is atop view of the device as arranged to protect a number of similarcircuits in which the bar a is substituted by the plate a. Fig. 3 is asectional view of Fig. 2 on the line 1 2.

Like letters of reference refer to like parts throughout.

In Fig. 1 two bars or tubes A and a, composed of a material capable ofexpansion when acted on by heat, such as vulcanite or hard rubber, areplaced parallel and firmly yoked together at one end by the yoke-piece 1by means of screws which pass through holes in the yoke-piece 1 into thesaid bars or tubes. The frame E consists of a strip of metal, bent inthe form shown in the drawings, and serves as a support for the bars ortubes A and a, being provided with holes through which said bars maypass without binding. Said bars are passed through said holes and fixedin position in frame E by the set-screw J, which clamps securely the baror tube a, near its extremity, to frame E. The frame E is rigidlysecured to base B, which is made of wood, porcelain,or other suitablenon-conducting material,by the screws N and N,which pass upward throughsaid base B into threaded holes in the lower part of said frame E. Theframe E is extended at one end in the form of a rectangular hook, on theinner side of which, near its extremity and in line with the axis of barA, is soldered or otherwise fixed the platinum contact-point C. 0n theuppermost side of said extension of frame E is fitted a bindingscrew K,by which is connected to said frame E one end of the fusible wire F. Theother end of fusible wire F is connected by the hinding-screw K to theconnecting-post H, which is secured to the base B, in connection withbinding-post D, by a screw passing upward through base B intobinding-post D. To the binding-post D is connected the line-wire L. Onthe free extremity of bar A and facing contact-point O is fixed thecontact-point O, which consists of a platinum-tipped piece of metalscrewed into the end of bar A. Said contact-point (3 is connected by thewire W to the binding-post D. Connected to binding-post D is theground-wire G. Spirally wound on the bar A is the German-silver orplatinoid wire M, said wire M being connected at one end to the frame Eat any convenient point 0 by solder or binding-screw, the remaining endof wire M being carried through base B and connected by connectingscrewto the binding-post D. To the binding-post D is connected the wire \V,leading to the instrument to be protected.

It is preferable that A should consist of a tube with a comparativelythin wall in order to possess a large surface in proportion to its mass,thus rendering it readily responsive to the heat generated by action ofthe current in the wire wound on its surface.

\Vhere it is necessary to protect a number of similar circuits, such aswould be the case in a telephone-exchange, the form of the device can bemodified, retaining its essential features, as heretofore described inFig. 1, such modification consisting,substantially,in the substitutionof a base-plate in place of bar or tube Ct. Figs. 2 and 3 show thismodification, of which Fig. 2 is a top view, and Fig. 3 a sectional viewon the line 1 2. In Figs. 2 and 3 the plate a, being composed of similarmaterial to that of bar or tube A, is secured to the base B by thescrews S S S, placed at intervals in a straight line midway of itswidth. Washers T, through which screws S S S pass, are placed betweenplate a and base Bin order to raise plate a slightly above base B. Oneend of bar or tube A is secured to plate a by means of an L-shaped pieceof metal E, to which it is attached by a screw which passes through saidpiece E into one end of bar A. The lower portion of supporting-piece Eis secured to plate Ct by means of a screw which passes through anoblong hole in piece E into plate a. The purpose of the oblong hole inpiece E is to allow of its adjustment before being clamped in position.The free end of bar A is provided with a contact-point C, as heretoforedescribed. Said bar-A passes loosely through ahole in supporting-pieceE. Said supporting-piece E, consisting substantially of a U shaped pieceof metal, is secured to the plate a by a screw, soldered or otherwisesecured to the inner side of supporting-piece E, and in line with theaxis of bar A and contactpoint C is the contact-point O. The support Eis provided with binding-screw K to secure one eudof fusible wire F.Wound on the bar A is the resistance-wire M, one end of which isconnected to the supporting-piece E, the other end of which is connectedto the binding-post D. Connecting the contact-point O with thebinding-post D is the wire .V. The con necting-post H is secured to thebase B and connected to the bindingpost D by a screw which passes upwardthrough base B into funding-post D. Post H is provided withbinding-screw K, by which is secured the other end of fusible wire F. Tothe binding-post D is connected the linewire L, and to the binding-postD is con nected the wire XV, leading to the instrument to be protected.Connected to binding-post D is the ground-wire G.

Normally the course of the circuit through the device is from the line Lto binding-post D, through fuse-wire F to frame E, to conceases 2inection 0, through resistance-wire M to binding-post D, through wire Wto protected instrument, thence to ground. Should the linewire becomecrossed with a high-voltage circuit, the course of the current is thesame as just described until the bar A becomes expanded by the heatgenerated in resistance- Wire M, when contact-point 0 makes contact withcontact point 0, thus establishing a ground connection between fusiblewire F and resistance-Wire M. The short circuit to earth thus formedreduces the resistance of the circuit between line and ground, enablingthe current to attain sufficient strength to melt fusible wire F, whichbreaks the curcuit. The circuit thus being broken, the current ceases toflow in the wire M. No further heat is generated therein, which allowsthe bar A to contract and withdraw the contact-point O away fromcontact-point O.

The function of the bar a, Fig. 1, which is composed of similar materialto that of which bar A is composed, is to effect a correction forexpansion or contraction in bar A due to variation in atmospherictemperature, thus preserving a constant length of air-gap between thecontact-points O and 0 so long as both bars A and a are subjected to anequal degree of temperature. The bar A being par allel to and yoked tobar a is held in position in the frame E at extremity of bar a by theset-screw J. Any expansion in bar A caused by variation in thetemperature of the surrounding air is compensated by a similar expansion in bar a, acting in an opposite direction, as the expanding ofbar a has a tendency to move bar A, with contact-point C, away fromcontact-point 0, whereas the expanding of bar A tends to bringcontact-point G toward con tact-point C. It is obvious,therefore, thatany equal expansion in bars A and a will not affect the relativeposition of contactpoints 0 and C; but should the bar A alone beexpanded,which would be the case should the wire M become hot due to anabnormal increase in the strength of the current circulating through it,the contact-point 0' would gradually approach and ultimately makecontact with contact-point 0.

Having fully described my invention,what I claim, and desire to secureby Letters Patent, is-

1. Two parallelheat-expansive bars or tubes having one each of theiradjacent ends rigidly connected by a yoke-piece, one of said bars ortubes having spirally wound on its surface a section of conductor andprovided at its free end with a contact-point, the other bar or tubesecured (at its end distant from yokepiece) to a standard carrying acontact-point facing contactpoint carried on bar, said standard securedto a base,said contactpoints being normally open and become closed whensaid bar on which conductor is wound is expanded in advance of othersaid bar by heat generated by action of current in said conductor.

2. A fusiblewire in circuit with a line-wire and protected instrument, aheat-expansive bar or tube secured at one end to a base and carrying acontact-point at its free extremity, facing said contact-point acontact-point carried on a standard secured to said base, a conductorspirally wound on said bar or tube and interposed in the circuit betweensaid fusible wire and protected instrument, one of said contact-pointsbeing electrically connected to circuit between fusible wire andconductor wound on said bar or tube, the other contact-point beingconnected to a ground-wire said contact-points being normally open andbecome closed when said bar or tube is expanded by heat generated insaid conductor by action of an abnormally-increased current circulatingtherein.

3. A fusible wire in circuit with a line-wire and protected instrument,two parallel heatcxpansive bars or tubes (preferably composed ofvulcanite or hard rubber) having one each of their adjacent ends rigidlyconnected by a yoke-piece, one of said bars or tubes being provided atits free end with a contact-point and having spirally wound on itssurface a conductor interposed in the circuit between said fusible wireand protected instrument, the other bar or tube secured (at its enddistant from yoke-piece) to a standard carrying a contact-point facingsaid contact-point car-- ried on bar, said standard secured to a base,one of said contact-points being electrically connected to the circuitbetween said fusible wire and said conductor which is wound on bar, theother contact-point being connected to a ground-wire, saidcontact-points normally being open and become closed when said bar ortube on which conductor is wound is expanded in advance of other saidbar or tube by heat generated in said conductor by action of anabnormally-increased current circulating therein.

a. Aheat-expansivc baror tube (preferably composed of vulcanite or hardrubber) carrying an electric-contact point at one of its ends andconnected at its other end by a yokepiece to a bar or tube composed ofsimilar material and secured to a standard carrying a contact-pointfacing contact-point on end .of said bar, a conductor spirally wound 011said bar or tube which carries contact-point, said contact-points beingnormally open so long as both bars or tubes are subjected to equaltemperatures but adapted to become closed by the expanding of bar ortube on which is wound conductor by heat generated in said conductorthrough action of current therein.

5. One or more similar heat-expansive bars or tubes (preferably composedof vulcanite or hard rubber) each of which being secured at one end to acommon base-plate composed of similar material to that of which saidbars or tubes are composed, said bars being parallel to said base andparallel to each other, the respective free ends of said bars or tubesbeing provided each with a contact-point said contact-points beingconnected to a groundwire, one or more standards (as many as there arebars) each carrying a contact-point said contact-points respectivelyfacing contactpoints on bars, each of said bars having spirally Wound onits surface a conductor one end of which being in electrical connectionwith its respective standard carrying contactpoint the respective endsof said conductors being connected each to a protected instrument,said'standards being connected respectively one end each to a fusiblewire the other respective ends of fusible Wires being respectivelyconnected each to a lineevire.

6. Aheat-expansive bar or tube (preferably composed of vulcanite or hardrubber) adapted to be expanded by heat generated in a con- F, O.ROBERTSON.

Witnesses:

IsIDoRE GRIFFIN, W. A. Wnnnnrr.

